Diameter of spinning chambers should be reduced, e.g. to 70 mm so as to achieve a substantial improvement of output of air-vortex spinners by increasing speed of the spinning chambers.
This results in a substantial increase in yarn breakage. To normalize the spinning process, it is necessary to shift twisting to the area of yarn formation so as to strengthen this area and to break-up rigidity triangles that prevent twisting from being shifted. The formation of such triangles becomes more likely with a decrease in the chamber diameter, increase in fiber length and with worse separation of fibers, Efficiency of prior art devices is inadequate for providing the desired twist in the zone of yarn formation and strengthening.
Yarn may be strengthened in the zone of its formation by imparting false twist in this zone. Projections are provided in the oulet tube of the open-end spinning device for imparting false twist.
Thus, SU pat. application No. 515844 discloses an open-end spinning device wherein an outlet tube mounted coaxially with a driven spinning chamber has a projection of a varying cross-section extending along a spiral uncoiling in the direction towards the spinning chamber, the projection being provided on the inner surface of the tube. The projection is made of a round-section wire which is secured to the inner surface of the tube by any known means.
However, the configuration of the projection spiral cannot ensure efficient shift of twisting into the yarn formation zone within the spinning chamber. This is due to the fact that the spiral has a constant value of the projection of an angle formed between a tangent line to the spiral and a line drawn at right angles to the longitudinal axis of the outlet tube on a plane drawn at right angles to the longitudinal axis of the tube.
This substantially lowers efficiency of shift of twisting in the yearn since the angle of turns in the yarn changes when false twist appears.
We have found that the value of the abovementioned projection of the angle is more than 40.degree. thus resulting in a less efficient penetration of the spiral projections into the yarn turns, i.e. the spiral would slip over the yarn without penetrating it so that the amount of false twist decreases.
With the wire diameters ensuring optimum conditions for its penetration into recesses between the yarn turns, the height of the projections above the funnel surface is so small that the yarn is not substantially separated from the funnel surface between the projections. The yarn is urged against the outlet tube surface between the projections by centrifugal forces and is subjected to crumpling so that the yarn cannot rotate about the longitudinal axis (this phenomenon is similar to the rolling friction). As a result, the yarn twist within the ballon zone is inadequate for normal spinning, and breakage increases.
With an increases in the wire diameter, conditions for penetration of the projection into the recesses between yearn turns are impaired so that the amount of shift of the twisting decreases. In addition, the thread is subjected to high shear and normal stresses in the zones of its fricitional engagement with the projections when it is bent at the projections, especially at points where the thread leaves the spiral and enters it, these stresses resulting in the destruction of thread structure and its crumpling.